01 -
Preheat the oven to 400°F. Grease a 9x13 inch baking dish and set aside.
02 -
Boil pasta in salted water until just al dente according to package instructions. Drain well and reserve.
03 -
Add diced potatoes to a saucepan and cover with water. Boil for 8 to 10 minutes until just tender, then drain thoroughly.
04 -
In a medium saucepan set over medium heat, melt the butter. Stir in the flour and cook, stirring constantly, for 1 minute.
05 -
Gradually whisk the milk into the flour mixture, stirring constantly until the sauce thickens, about 4 minutes. Remove from heat and stir in the sour cream, cheddar cheese, mozzarella cheese, garlic powder, onion powder, salt, and black pepper until the cheeses have melted and the sauce is smooth.
06 -
In a large mixing bowl, combine cooked pasta, drained potatoes, half of the bacon, half of the scallions, and the prepared cheese sauce. Mix gently until evenly coated.
07 -
Spread the pasta mixture evenly in the prepared baking dish. Sprinkle the remaining cheddar cheese and bacon over the top.
08 -
Bake for 18 to 20 minutes or until bubbly and golden brown on top.
09 -
Remove from the oven. Sprinkle with remaining scallions and chopped chives just before serving.